INTRODUCTIONIn electronics, modulation is the process of varying one or more properties of a high frequency periodic waveform, called the carrier signal, with respect to a modulating signal. This is done in a similar fashion as a musician may modulate a tone (a periodic waveform) from a musical instrument by varying its volume, timing and pitch. The three key parameters of a periodic waveform are its amplitude ("volume"), its phase ("timing") and its frequency ("pitch"), all of which can be modified in accordance with a low frequency signal to obtain the modulated signal. Typically a high-frequency sinusoid waveform is used as carrier signal, but a square wave pulse train may also occur. Aim

The aim of digital modulation is to transfer a digital bit stream over an analog passband channel, for example over the public switched telephone network (where a bandpass filter limits the frequency range to between 300 and 3400 Hz), or over a limited radio frequency band. The aim of analog modulation is to transfer an analog baseband (or lowpass) signal, for example an audio signal or TV signal, over an analog passband channel, for example a limited radio frequency band or a cable TV network channel.

| |

2 Analog modulation methods
In analog modulation, the modulation is applied continuously in response to the analog information signal. [pic]
[pic]
A low-frequency message signal (top) may be carried by an AM or FM radio wave. Common analog modulation techniques are: • Amplitude modulation (AM) (here the amplitude of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal) o Double-sideband modulation (DSB)

• Angle modulation o Frequency modulation (FM) (here the frequency of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal) o Phase modulation (PM) (here the phase shift of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal) The accompanying figure shows the results of (amplitude-)modulating a signal onto a carrier (both of which are sine waves). At any point along the y-axis, the amplitude of the modulated signal is equal to the sum of the carrier signal and the modulating signal amplitudes. [pic]

[pic]
Simple example of amplitude modulation.
3 Digital modulation methodsIn digital modulation, an analog carrier signal is modulated by a digital bit stream. Digital modulation methods can be considered as digital-to-analog conversion, and the corresponding demodulation or detection as analog-to-digital conversion. The changes in the carrier signal are chosen from a finite number of M alternative symbols (the modulation alphabet). [pic]

[pic]
Schematic of 4 baud (8 bps) data link.
A simple example: A telephone line is designed for transferring...

YOU MAY ALSO FIND THESE DOCUMENTS HELPFUL

...Digitalmodulation
differents kind and aplications form them.
DigitalModulationTechniques
The techniques used to modulate digital information so that it can be transmitted via microwave, satellite or down a cable pair are different to that of analogue transmission. The data transmitted via satellite or microwave is transmitted as an analogue signal. The techniques used to transmit analogue signals are used to transmit digital signals. The problem is to convert the digital signals to a form that can be treated as an analogue signal that is then in the appropriate form to either be transmitted down a twisted cable pair or applied to the RF stage where is modulated to a frequency that can be transmitted via microwave or satellite.
The equipment that is used to convert digital signals into analogue format is a modem. The word modem is made up of the words “modulator” and “demodulator”.
A modem accepts a serial data stream and converts it into an analogue format that matches the transmission medium.
There are many different modulationtechniques that can be utilised in a modem. These techniques are:
• Amplitude shift key modulation (ASK)
• Frequency shift key modulation (FSK)
•...

...DCE at point A.
4. The transmission channel between points A and B.
5. The DCE at point B.
6. The DCE - DTE interface at point B.
7. The DTE at point B.
DIGITALMODULATION
Phase Shift Keying
-One of the simplest forms of digitalmodulation is binary or Bi-Phase Shift Keying (BPSK). One application where this is used is for deep space telemetry. The phase of a constant amplitude carrier signal moves between zero and 180 degrees. On an I and Q diagram, the I state has two different values. There are two possible locations in the state diagram, so a binary one or zero can be sent. The symbol rate is one bit per symbol. A more common type of phase modulation is Quadrature Phase Shift Keying (QPSK). It is used extensively in applications including CDMA (Code Division Multiple Access) cellular service, wireless local loop, Iridium (a voice/data satellite system) and DVB-S (Digital Video Broadcasting — Satellite).
Frequency Shift Keying
Frequency modulation and phase modulation are closely related. A static frequency shift of +1 Hz means that the phase is constantly advancing at the rate of 360 degrees per second (2 π rad/sec), relative to the phase of the unshifted signal. FSK (Frequency Shift Keying) is used in many applications including cordless and paging systems. Some of the cordless systems include DECT (Digital Enhanced Cordless...

...Comparative Study of DigitalModulationTechniques in WIMAX
Umesh Sharma
Abstract: - The migration to 4G networks will bring a new level of expectation to wireless communications. As after digital wireless revolution made mobile phones available for everyone, the higher speeds and packet delivery of 4G networks will make high quality multimedia available everywhere. The key to achieving this higher level of service delivery is a new air interface. Orthogonal Frequency Division Multiplexing (OFDM) is an alternative wireless modulation technology to CDMA. OFDM is a digitalmodulation and multiplexing technique. In this paper, we have discussed various digitalmodulationtechniques such as BPSK (2bits), QPSK (4 bits), QAM, 16 QAM and 64 QAM. We have designed simulation environment in MATLAB with various configurations of OFDM technique. The main objective of our work is to measure Bit Error Rate with different modulation schemes and come to the best configuration to achieve better utilization of bandwidth. We have studied existing configurations with analog and digitalmodulationtechniques and compared the results. The driving force behind the need to satisfy this requirement is the explosion in mobile telephone, Internet and multimedia services coupled...

...CS3282 Digital Comms
9.1
2 May’06 / BMGC
Multi-level digitalmodulation & demodulation.
9.1. Introduction: So far, in looking at carrier modulated data transmission, we have concentrated mainly on binary signalling using simple forms of ASK, FSK and PSK. With a suitable pulse-shape, binary signalling can achieve a bandwidth efficiency of up to 2 bits/second per Hz using real unipolar pulses (base-band equivalent of ASK) or real bipolar pulses (base-band equivalent of PSK) at base-band. Since multiplying the base-band signal by a sinusoidal carrier doubles its bandwidth, the maximum band-width efficiency of binary ASK and binary PSK becomes one bit/second/Hz . With this band-width efficiency, a computer modem could achieve a maximum of about 3.1 kb/s over a 300-3400 kHz domestic telephone link. This is less than one tenth of what we know to be achievable. A similar calculation for the bandwidth-efficiency of binary FSK is a little more complicated, but if we take the frequency spacing used by MSK, i.e. 1/(2T) Hz, which is the minimum spacing compatible with the desirable highly property of 'orthogonality' between the 2 symbols, we may expect to achieve a maximum of slightly less than 2 bit/second per Hz. To increase the band-width efficiency over what can be achieved with binary signalling we must use multi-level modulation schemes where each symbol represents more than one bit. 9.2. Multi-level ASK and Gray...

...
Kirk Samuda
Institute of Advanced Technology
Devry University
September 2005
Advanced Telecommunication
To fully understand the advantages of the various modulationtechniques of analog
signals, I think it’s important to understand the very basic premise on which modulation
exist. Allow me the privilege of starting with the basic function of any communication
system, which is transmitting information from one point to another. It may appear like a
simple process, however it is not. Consideration must be given to a conversation between
two people within close proximity, one speaks and another listens.
We already can observe some basic concepts of modulation, which reflects the power
of information as the sound of one person’s voice is dependent on the capacity of the lungs
of each individual reflected as a whisper, talk, or scream. The transmission medium that
carries sound from one person to another is considered either the air or free space.
It must be noted that the person who speaks (whoever that is) can be considered
the transmitter and the person listening is the receiver. Hence as the information, words,
sound is about to leaves the first person’s mouth it needs to be converted or changed
(modulate) then transmitted to the ears of the listener. The listener (receiver) must then
interpret the sounds heard or transmitted...

...APCOMS |
DIGITAL IMAGE PROCESSING |
ASSIGMNENT |
|
SIR SHAHID ISMAIL |
29-May-13 |
|
GROUP MEMBERS:
USAID SHUAIB F-3313
AHMED TAUQIR F-3324
HAMMAD SHEIKH F-3325
GROUP MEMBERS:
USAID SHUAIB F-3313
AHMED TAUQIR F-3324
HAMMAD SHEIKH F-3325
Representation
Segmentation techniques yield raw data in the form of pixels along a boundary or pixels contained in a region. These data sometimes are used directly to obtain descriptors. Standard uses techniques to compute more useful data (descriptors) from the raw data in order to decrease the size of data.
Chain Codes
A chain code is a lossless compression algorithm for monochrome images. The basic principle of chain codes is to separately encode each connected component, or "blob", in the image. For each such region, a point on the boundary is selected and its coordinates are transmitted. The encoder then moves along the boundary of the region and, at each step, transmits a symbol representing the direction of this movement. This continues until the encoder returns to the starting position, at which point the blob has been completely described, and encoding continues with the next blob in the image.
This encoding method is particularly effective for images consisting of a reasonably small number of large connected components.
Some popular chain codes include the Freeman Chain Code of Eight Directions (FCCE), Vertex Chain Code (VCC), Three Orthogonal...

...﻿Amplitude Modulation
A carrier is used to make the wavelength smaller for practical transmission and to permit multiplexing.
The spectrum is used to measure bandwidth (the range of frequencies) and the efficiency (the power in the side-bands compared to the total power)
Bandwidth can be predicted using BW = 2 fm where fm = the maximum modulating frequency
Efficiency depends only on the modulating index, m (the fraction of the carrier you modulate by)
AM is limited to 33% efficiency because the modulation index cannot be increased to > 1.0 without introducing distortion in the receiver.
1. Carrier signal equations
Looking at the theory, it is possible to describe the carrier in terms of a sine wave as follows:
π
C (t) = C sin (ωc + φ)
Where:
carrier frequency in Hertz is equal to ωc / 2 π
C is the carrier amplitude
φ is the phase of the signal at the start of the reference time
Both C and φ can be omitted to simplify the equation by changing C to "1" and φ to "0".
2. Modulating signal equations
The modulating waveform can either be a single tone. This can be represented by a cosine waveform, or the modulating waveform could be a wide variety of frequencies - these can be represented by a series of cosine waveforms added together in a linear fashion.
For the initial look at how the signal is formed, it is easiest to look at the equation for a simple single tone waveform and then expand the concept to cover the...